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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"><head>	<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />	<style type="text/css">	body { font-family: Verdana, Arial, Helvetica, sans-serif;}	a.at-term {	font-style: italic; }	</style>	<title>Mapping Functions</title>	<meta name="Generator" content="ATutor">	<meta name="Keywords" content=""></head><body> <h3>Mapping process grid coordinates to ranks</h3>

<p class="codelang">C:</p>

<pre><code>int MPI_Cart_rank(MPI_Comm comm, int *coords, int *rank)</code></pre>

<p class="codelang">Fortran:</p>

<pre><code>INTEGER    COMM, COORDS(*), RANK, IERROR
CALL MPI_CART_RANK(COMM, COORDS, RANK, IERROR)</code></pre>


<h3>Mapping ranks to process grid coordinates</h3>

<p class="codelang">C:</p>

<pre><code>int MPI_Cart_coords(MPI_Comm comm, int rank, int maxdims, int *coords)</code></pre>


<p class="codelang">Fortran:</p>

<pre><code>INTEGER    COMM, RANK, MAXDIMS, COORDS(*), IERROR
CALL MPI_CART_RANK(COMM, RANK, MAXDIMS, COORDS, IERROR)</code></pre>


<h3>Sample Program - C</h3>

      <pre><code>#include &lt;mpi.h&gt;
#include &lt;stdio.h&gt;
#define TRUE 1
#define FALSE 0
/* Run with 12 processes */
int main(int argc, char *argv[]) {
  int rank;
  MPI_Comm vu;
  int dim[2],period[2],reorder;
  int coord[2],id;
  MPI_Init(&amp;argc, &amp;argv);
  MPI_Comm_rank(MPI_COMM_WORLD,&amp;rank);
  dim[0]=4; dim[1]=3;
  period[0]=TRUE; period[1]=FALSE;
  reorder=TRUE;
  MPI_Cart_create(MPI_COMM_WORLD,2,dim,period,reorder,&amp;vu);

  if(rank==5){
    MPI_Cart_coords(vu,rank,2,coord);
    printf("P:%d My coordinates are %d %d\n",rank,coord[0],coord[1]);
  }

  if(rank==0) {
     coord[0]=3; coord[1]=1;
     MPI_Cart_rank(vu,coord,&amp;id);
     printf("The processor at position (%d, %d) has rank %d\n",coord[0],coord[1],id);
  }
  MPI_Finalize();
}</code></pre>

<h3>Program Output:</h3>
<pre><code>The processor at position (3,1) has rank 10
P:5 My coordinates are 1 2</code></pre>

<h3>Sample Program - Fortran</h3>

<pre><code>      PROGRAM Cartesian
C
C Run with 12 processes
C
      INCLUDE 'mpif.h'
      INTEGER err, rank, size
      integer vu,dim(2),coord(2),id
      logical period(2),reorder
      CALL MPI_INIT(err)
      CALL MPI_COMM_RANK(MPI_COMM_WORLD,rank,err)
      CALL MPI_COMM_SIZE(MPI_COMM_WORLD,size,err)
      dim(1)=4
      dim(2)=3
      period(1)=.true.
      period(2)=.false.
      reorder=.true.
      call MPI_CART_CREATE(MPI_COMM_WORLD,2,dim,period,reorder,vu,err)

      if(rank.eq.5) then
          call MPI_CART_COORDS(vu,rank,2,coord,err)
          print*,'P:',rank,' my coordinates are',coord
      end if

      if(rank.eq.0) then
          coord(1)=3
          coord(2)=1
          call MPI_CART_RANK(vu,coord,id,err)
          print*,'P:',rank,' processor at position',coord,' is',id
      end if

      CALL MPI_FINALIZE(err)
      END</code></pre>

<h3>Program output:</h3>
<pre><code>P:5 my coordinates are 1, 2
P:0 processor at position 3, 1 is 10</code></pre></body></html>
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